We have handy functions to access GPR. Use gen_store_gpr() for
Move From HI/LO Register and gen_load_gpr() for Move To opcodes.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210214175912.732946-8-f4bug@amsat.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>